1. Field of the Invention
The invention relates to an image forming apparatus using an electrophotographic printing method or an electrostatic recording method, and particularly to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus.
2. Description of Related Art
In image forming apparatus such as a printing machine, a copying machine and a printer, image outputs higher in quality of image have come to be required. As a guide to the high quality of image, there is the glossiness of a printed image. Particularly in the case of an image such as a photograph or an illustration, there is the tendency that an image of high glossiness is liked.
What determines the glossiness of an image is the fixing time or the fixing temperature in a fixing apparatus for fixing an unfixed toner image on a sheet such as paper or OHP film, i.e., the amount of heat applied to the sheet during fixing. By the amount of heat applied to the sheet during fixing, the fused state of a toner or the permeability of the toner into the sheet is changed, whereby the gloss of the image is changed. Usually, the greater becomes the amount of applied heat, the higher becomes the gloss of the image.
So, in order to realize the glossiness desired by a user, there has been devised an image forming apparatus provided with a plurality of fixing devices.
In Japanese Patent Application Laid-open No. 2003-167459 and Japanese Patent Application Laid-open No. 2000-221821, it is described to effect image forming by the use of a plurality of fixing. apparatuses. Design is made such that of the plurality of fixing apparatuses, the number of fixing apparatuses to be used is automatically switched depending on such conditions as the kind of the paper selected by the user, and whether the copy image is monochromatic or multi-colored.
Particularly, in Japanese Patent Application Laid-open No. 2000-221821, there are disclosed two kinds of constructions, i.e., (i) a case where the user sets glossiness, and (ii) glossiness is automatically determined by the material of a sheet. In the case (i), even if the set gloss mode is high gloss, when the glossiness of a sheet itself is low, the outputted image is merely of the high gloss when that sheet is used. Therefore, it differs from the actually desired glossiness of the output image. In the case (ii), the glossiness is primarily determined by the material or basis weight of the sheet and therefore, it may also differ from the glossiness of the output image actually desired by the user.
If the output image of glossiness differing from the glossiness desired by the user, as described above, is intactly printed in a number of copies, there will result a great deal of products low in degree of satisfaction. That is, in the conventional construction, wasteful prints are outputted, and an improvement in usability is demanded.